JPH02199033A - Production of optical glass - Google Patents

Abstract

PURPOSE:To obtain optically uniform and large-sized optical glass in good dimensional accuracy by adding fine particles of SiO2 having larger particle diameter to a sol solution prepared by hydrolyzing a silicon alkoxide, then gelatinizing the sol solution, drying to give porous gel material and heat-treating the material. CONSTITUTION:A silicon alkoxide Si(OR)4 (R is alkyl group) is hydrolyzed to give a sol solution containing fine particles of SiO2 having <=0.005mu-<0.03mum average particle diameter, the sol solution is mixed with fine particles of SiO2 having >=0.03mum average particle diameter, successively gelatinized and dried to give a porous gel material. Then the porous gel material is treated at high temperature to give a transparent glass material. When the sol solution after being blended with the fine particles of SiO2 having >=0.03mum average particle diameter is mixed with an alkoxide: Si(OR)4-nFn (0<n<=4) wherein at least one alkoxy group of the silicon alkoxide is replaced with fluorine, gel strength can be raised. The amount of the fine particles of SiO2 having >=0.03mum average particle diameter added is preferably >=10mol% (upper limit is about 70mol%) based on the whole silicon atoms.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method of manufacturing optical glass.

More specifically, the present invention relates to a method for manufacturing a large fluorine-doped quartz glass body that is optically homogeneous and free from irregularities such as cracks and bubbles.

(Prior Art) As a method for producing high-purity glass, a sol-gel method is known in which a Si02 glass polymer is produced in a solution by hydrolysis and condensation of silicon alkoxide. In the sol-gel method, glass polymers with different structures can be obtained by hydrolysis under an appropriate catalyst. For example, when an acidic catalyst such as hydrochloric acid is added, a linear polymer is produced. do. On the other hand, when a basic catalyst such as ammonia is used, the average particle size is 0.001 to 0.3 μm.
It is possible to obtain a finely divided polymer having a uniform particle size distribution over a wide range of . As a method for producing fluorine-doped quartz glass using a sol-gel method, a liquid phase fluorine addition method has been proposed by the present inventors.

FIG. 5 shows the steps of this fluorine-added quartz glass manufacturing method. In this method, alkoxide 4, in which some of the alkoxy groups are substituted with fluorine, is added as a fluorine additive to sol solution 1 obtained by hydrolyzing silicon alkoxide. In addition, a fluorine-doped SiO2 sol solution 5 is formed, which is then converted into a gel 6 and dried to form a porous gel body 7, which is then treated at high temperature to obtain a transparent fluorine-doped quartz glass body 8.

According to this method, a homogeneous fluorine-doped quartz glass body containing few impurities such as metals and OH groups and free from irregularities such as bubbles can be manufactured with good controllability of the refractive index.

(Problems to be Solved by the Invention) Conventionally, this method uses a sol solution containing SiO2 fine particles with a narrow particle size distribution, which has caused the following problems. When the average particle size of the 5102 fine particles is 0.03 μm or less, the pore size of the gel is small, so when the solvent and water are evaporated in the drying process, a large stress is generated inside the gel body, causing cracks in the gel body. It was easy to occur. For this reason,
A glass body having dimensions of approximately 20 mm in diameter and 50 mm or more in length has not been obtained. On the other hand, the average particle size is 0.0
When SiO2 fine particles of 3 μm or more are used, the gel body is soft and deformed during the drying process, making it difficult to manufacture a glass body of a predetermined shape with good dimensional accuracy.

The present invention has been made in view of the above-mentioned problems, and provides a method for manufacturing an optically homogeneous large-sized fluorine-doped quartz glass body with high dimensional accuracy.

(Means for solving the problem) The manufacturing method of the present invention includes silicon alkoxide Si (
OR) 4 (R is an alkyl group) sol solution containing SiO2 fine particles with an average particle size of 0.005 μm or more and less than 0.03 μm by hydrolysis, and S with an average particle size of 0.03 μm or more.
i02 microparticles are mixed, followed by gelation and drying,
It is characterized by forming a porous gel body and treating it at high temperature to obtain a transparent glass body.

Further, in the second manufacturing method of the present invention, an alkoxide Si (OR)4-nFn in which at least one of the alkoxy groups of silicon alkoxide is substituted with fluorine is added to the sol solution after mixing the SiO2 fine particles of 0.03 μm or more. (
0<n≦4).

Further, according to the present invention, the amount of Si02 fine particles having an average particle size of 0.03 μm or more added is 10 mol % or more based on the total silicon atoms.

The present invention will be explained in more detail.

The method for manufacturing optical glass of the present invention is shown in FIG.

As is clear from FIG. 1, according to the method for producing optical glass according to the present invention, the average particle size obtained by hydrolyzing Si(OR)4 (R is an alkyl group) is 0.005 μm or more and 0.03 ttm. Sol solution containing SiO2 fine particles of less than 1
and Si02 fine particles 2 with an average particle size of 0.03 μm or more, and optionally add Si (OR)4 to this SiO2 solution 3.
- Add and mix nFn4. The fluorine-added Si02 sol solution 5 to which a fluorine-substituted alkoxide is optionally added is left to stand to form a gel 6, and then dried to form a porous gel body 7. This is subjected to high temperature treatment to obtain a transparent glass body 8.

5t02 contained in the S i 02 sol solution as described above
The average particle diameter of the fine particles is 0.005 μm or more and less than 0.03 μm. The average particle size of this Si02 fine particles is 0.005
If it is less than .mu.m, it is difficult to produce a glass that is homogeneous and free from irregularities such as bubbles, as is clear from the examples described later.

In such a sol solution, S with an average particle size of 0.03 μm or more is added.
Add i02 microparticles. These fine particles are added to prevent cracking during the drying process, etc.
If the average particle size is less than 0.03 μm, it is difficult to exhibit effects such as crack prevention, but on the other hand, the upper limit of the average particle size of the particles is preferably 0.1 μm. This is because if it exceeds 0.1 μm, there is a risk that fine particles will precipitate in the sol solution.

The amount of the fine particles added is preferably 10 mol % or more. If it is less than 10 mol%, cracks may occur during the drying process. On the other hand, the preferable upper limit of the amount added is 70 mol%. This is because the improvement effect does not change even if it is added in an amount exceeding 70 mol%.

In the present invention, Si
Add an alkoxide represented by (OR)4-nFn. This fluorine-substituted alkoxide is added to increase gel strength, and its preferred amount is 1 to 70 mol%.
It is. If it is less than 1 mol%, there is no effect of addition, while 7
If it exceeds 0 mol%, polycondensation occurs due to the catalytic effect of fluorine, producing secondary particles. This results in the disadvantage that the particle size becomes large and transparent glass cannot be formed at temperatures below 1500'C.

In the alkoxides and fluorine-substituted alkoxides mentioned above, R is an alkyl group, preferably a lower alkyl group such as methyl, ethyl, propyl, butyl.

(Function) The method of the present invention includes Si having a larger particle size in the sol solution.
By adding 02 fine particles, the mechanical strength of the gel can be increased, making it possible to manufacture large fluorine-doped quartz glass bodies with high dimensional accuracy without cracking during the drying process. The glass obtained by this method is characterized by having no residual irregularities such as bubbles and having very high optical homogeneity.

Hereinafter, this will be explained in detail using examples.

(Example 1) Tetraethoxysilane Sl(OC2H3)4 was hydrolyzed under an ammonia catalyst to form S with an average particle size of 0°01 μm.
A sol solution containing i02 fine particles was prepared. This sol solution has an average particle size of 0.01
Add Si02 microparticle powder of μm, 0.03 μm, 0°1 μm, add 2 mol% of Si (OC2H5)3F as a fluorine additive, mix well, gel in a container, slowly dry, and create a porous A gel body (diameter 12 mm, length 50 mm) was obtained.

The bending strength of the produced dried gel body was evaluated by a three-point bending test. The results are shown in Figure 2. When fine particles of 0.01 μm, which are equal to the particle size of SiO2 particles made from alkoxide, were added, the strength of the gel was constant, but the average particle size was 0.03 μm, It was found that when fine particles of 0.1 μm were added, the strength of the dried gel body increased as the amount added increased. Average particle size 0゜1μ
When 10 mol % or more of m fine particles were added, the bending strength was twice that of the case without addition.

This example revealed that the mechanical strength of the gel body was increased by adding SiO2 fine particles powder with a larger particle size to a sol solution containing SiO2 fine particles prepared by hydrolysis of alkoxide. .

(Example 2) Tetraethoxysilane Si (OC2H5)4 was hydrolyzed under an ammonia catalyst to prepare a sol solution containing Si02 fine particles with an average particle size of 0.01 μm. This sol solution has an average particle size of 0.1 μm produced by a gas phase method.
After adding 10 mol % of Si (OC2H5)3F as a fluorine additive and thoroughly mixing, the mixture was gelled in a container and slowly dried to obtain a porous gel body. This gel body was treated at a high temperature of 1350°C to create a transparent fluorine-doped quartz glass body (diameter 45 to 5 mm).
5 mm, length 135-160 mm).

Figure 3 shows the density of cracks that occurred in the transparent glass body (the value obtained by dividing the total number of cracks that occurred in the glass body by the volume of the glass body).
As shown in Figure 0, which shows the relationship between the amount of SiO2 particles added and the amount of SiO2 particles added using the vapor phase method, the density of cracks decreases as the amount added increases, and fluorine addition causes no cracks at all when the amount added is 10 mol% or more. It turned out that a quartz glass rod was obtained.

This example revealed that a crack-free fluorine-doped silica glass body can be produced by adding SiO2 fine particle powder with a larger particle size to a sol solution containing SiO2 fine particles prepared by hydrolysis of alkoxide. . As shown in Example 1, it is considered that the mechanical strength of the gel was increased and cracking could be prevented.

(Example 3) Tetraethoxysilane Si (OC2H5)4 was hydrolyzed under an ammonia catalyst, and the average particle size was 0.003.0.
．． 005.3 containing SiO2 fine particles of 0.01 μm
Various types of sol solutions were prepared. Each of these sol solutions had an average particle size of 0.1% by 70 mol% and was prepared by a gas phase method.
Add 20 mol% of μm SiO2 fine particle powder, add 10 mol% of Si(OC2H3)3F as a fluorine additive, mix thoroughly, gel in a container, and slowly dry to form three types of porous gels. I got a body. These gel bodies were heated to 1350℃
After high temperature treatment, a fluorine-doped quartz glass body with a diameter of 10 m is produced.
m, length 80 mm) was obtained.

As a result, glass made by adding fine particle powder to a sol solution containing fine particles with an average particle size of 0.003 μm has the following properties:
Remaining air bubbles were observed. On the other hand, the average particle size is 0.005μ
The glass produced by adding fine particle powder to a sol solution of m or more was extremely homogeneous, and no irregularities such as bubbles were observed at all.

From this example, SiO with an average particle size of 0.005 μm or more
2. S i with larger particle size is added to the sol solution containing fine particles.
It has become clear that by adding 02 fine particles, a very homogeneous fluorine-doped quartz glass body without bubbles or cracks can be produced.

(Example 4) In place of the SiO2 fine particle powder produced by the gas phase method, a sol solution containing Si02 fine particles with an average particle size of 0.03 μm, which was obtained by hydrolyzing alkoxide under an ammonia catalyst, was added. An experiment similar to Example 2 was conducted.

Figure 4 shows a fluorine-doped quartz glass body (43 to 48 m in diameter).
This graph shows the relationship between the density of cracks (with a length of 130 to 150 mm) and the amount of SiO2 fine particles added with an average particle size of 0.03 μm, as in Example 2. It has been found that a fluorine-doped quartz glass rod with a reduced density and no cracking can be obtained when the addition amount is 40 mol% or more.

From this example, by adding a sol solution containing SiO2 fine particles with a larger particle size prepared by hydrolysis of alkoxide, it was found that crack-free fluorine was produced in the same manner as when fine particle powder prepared by a vapor phase method was added. It has become clear that a doped silica glass body can be produced.

(Example 5) In the same manner as in Example 4, 50 mol% of fine particles with an average particle size of 0.01 μm and 4 mol% of fine particles with an average particle size of 0.03 μm were prepared.
Fluorine additive S is added to the SiO2 sol solution containing 0 mol%.
i (OC2H5)3F was added in an amount of 10 mol%, mixed thoroughly, gelled in a petri dish, and slowly dried.
A porous gel plate was obtained. This gel plate was subjected to high temperature treatment at 1350° C. to obtain a transparent fluorine-doped quartz glass plate (diameter 60 mm, thickness 10 mm) with no cracks or bubbles.

(Example 6) In order to evaluate the optical quality of the produced fluorine-doped silica glass, an optical fiber was produced.

A sol solution prepared in exactly the same manner as in Example 5 was gelled in a cylindrical container, dried, and then treated at a high temperature of 1350°C to form a transparent fluorine-doped quartz glass tube (relative refractive index difference with respect to quartz glass). 0.38%, outer diameter 25mm, inner diameter 15m
m, length 200 mm) was obtained. This fluorine-doped quartz glass tube is heated to evaporate fluorine from the surface, creating a diffusion layer with a low fluorine concentration on the inner surface of the tube.Then, this glass tube is solidified and a high refractive index region (core ) was obtained. This base material was drawn at high temperature to obtain a single mode optical fiber.

The obtained fluorine-doped quartz glass tube has a uniform inner diameter, outer diameter, and wall thickness, and it has been found that this method can produce a glass tube with high dimensional accuracy.The optical fiber produced has a loss of 1. It was as small as 0.3 dB/km at 60 μm, and it became clear that the produced glass was optically homogeneous.

(Effect of the invention) As explained above, Si02 fine particles having a larger particle size are added to a sol solution containing Si02 fine particles with an average particle size of 0.005 μm or more and less than 0.03 μm, which is prepared by hydrolyzing alkoxide. As a result, an optically homogeneous fluorine-doped silica glass body, which is more than twice as large as the glass body obtained by conventional methods, can be produced with high dimensional accuracy.
can be manufactured.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the steps of the optical glass manufacturing method of the present invention, FIG. 2 is a diagram showing the relationship between the amount of S i 02 fine particles added and the bending strength of the dry gel body produced by the vapor phase method, and FIG. The figure shows the relationship between the density of cracks occurring in a fluorine-doped quartz glass body and the amount of 5102 fine particles added with an average particle size of 0.1 μm. Figure 4 shows the relationship between the density of cracks occurring in a fluorine-doped quartz glass body and , a diagram showing the relationship between the amount of S i 02 fine particles added having an average particle diameter of 0.03 μm, and FIG. 5 is a diagram showing the steps of a conventional method for manufacturing fluorine-doped silica glass.

Claims (3)

[Claims] (1) The average particle size of hydrolyzed silicon alkoxide Si(OR)_4 (R is an alkyl group) is 0.005 μm
A sol solution containing SiO_2 fine particles with a size of less than 0.03 μm and SiO_2 fine particles with an average particle size of 0.03 μm or more are mixed, and then gelled and dried to form a porous gel body, which is then treated at high temperature. , a method for producing optical glass characterized by obtaining a transparent glass body. (2) The sol solution containing SiO_2 fine particles with an average particle size of 0.03 μm or more is alkoxide Si(OR)_4_−_nF_n (0<n≦4) in which at least one of the alkoxy groups of silicon alkoxide is replaced with fluorine. The method for producing optical glass according to claim 1, wherein the optical glass is added. (3) Claim 1 or 2, characterized in that the amount of SiO_2 fine particles with an average particle size of 0.03 μm or more is 10 mol% or more based on the total silicon atoms.
A method for producing optical glass as described in Section 1.